The present invention relates to an electronically controlled fuel injection system for controlling a fuel quantity to be injected into each cylinder of a diesel engine by a fuel injection pump, and in particular to such a system for controlling an actuator of the fuel injection pump by means of a servo mechanism so that a fuel quantity adjusting member operatively responsive to the energization of the actuator is controlled for a high precision positioning thereof.
In a prior art electronically controlled fuel injection system, a PID (Proportional Integral Differential) control process is employed in a positioning servo system for the purpose of controlling so that an actual position of the fuel injection adjustment member coincides with a desired position thereof corresponding to an optimum injection fuel quantity, derived as a function of engine operating conditions determined on the basis of engine operating parameters. One example of such a PID control servo system is disclosed in Japanese Laid-Open Patent Application No. 59-25047.
The factors generally required to position servo systems, include accuracy, response time, stabilization and overshoot amount. In order to increase the capability and performance thereof, it is important not only that each of the factors is enhanced or optimized, but also that these factors be simultaneously satisfied without making any of them worse.
However, according to the PID control, it is impossble to simultaneously satisfy the above-described factors. For example, an increase in proportional gain for a quick response results in an excess of overshoot and also in a reduction of stability. In addition, it is difficult to obtain an appropriate servo characteristic because of the non-linear characteristic of the controlled system, i.e., actuator.